Do nanoenergetic particles remain nano-sized during combustion?

Chakraborty, Purnendu; Zachariah, Michael R.

doi:10.1016/j.combustflame.2013.10.017

Cited by 116 publications

(61 citation statements)

References 23 publications

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“…Recent advances in particle production techniques have brought fuel particle sizes down to the nano-scale, and many have shown that Al nanoparticles (nAl) exhibit higher reactivity than Al microparticles (µAl). There are several potential mechanisms explaining the increase in reactivity for nAl [8][9][10][11][12][13][14][15][16]. However, interest is now shifting towards utilizing what is understood about the mechanisms promoting optimal reactivity in nAl particles towards engineering more reactive µAl particles.…”

Section: Introductionmentioning

confidence: 99%

A slice of an aluminum particle: Examining grains, strain and reactivity

McCollum

Smith

Hill

et al. 2016

Combustion and Flame

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Micron-scale aluminum (Al) particles are plagued by incomplete combustion that inhibits their reactivity. One approach to improving reactivity is to anneal Al particles to increase dilatational (volumetric) strain which has also been linked to increased combustion performance. While optimal annealing temperatures have been identified (roughly 300 °C), little is known about cooling rate effects on particle combustion performance. This study examines the effect of quenching after annealing Al microparticles to 100, 200 and 300 o C on intra-particle dilatational strain and reactivity. Synchrotron X-ray diffraction analysis of the particles reveals the cooling rates in the range from 0.007 to 0.38 K/s have little effect on the dilatational strain of the aluminum-core, alumina-shell particles. The annealed and quenched Al particles were then combined with a metal oxidizer (copper oxide) to examine reactivity. Flame propagation experiments follow the same trend: flame speeds are unchanged until a critical annealing temperature of 300 °C is reached and performance is maintained for each annealing temperature regardless of cooling rate. These results show that altering the mechanical properties and combustion performance of Al particles is strongly dependent on the annealing temperature and unchanged with variation in cooling rate. The contributions from elastic and plastic deformation mechanisms on strain are also considered and additional experimental results are shown on the microstructure of an Al particle. Focused ion beam milling of an Al particle to electron transparency was combined with transmission electron microscope imaging in order to examine the microstructure of the Al particles. This confirmed that the Al microparticles have a polycrystalline structure shown by grains all exceeding 100 nm in size.

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Section: Introductionmentioning

confidence: 99%

A slice of an aluminum particle: Examining grains, strain and reactivity

McCollum

Smith

Hill

et al. 2016

Combustion and Flame

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“…Towards this end, many have proposed new Al synthesis strategies: such as altering the native aluminum oxide (Al 2 O 3 ) coating with another passivating agent such as alkenes [1] or applying self-assembled monolayers (SAM) to the particle surface [2]. Various explanations for Al oxidation mechanisms have also been proposed, each strongly tied to the ignition mechanism and heating rate [3]- [11]. All theories share a common theme for mass transport of fuel and oxidizer, but differ in how that diffusion is achieved (i.e., via (a) dispersion [3], [4], (b) phase changes in the polymorphous passivation shell [5]- [7] , (c) reactive sintering [8], (d) pressure gradient driven processes [9], [10], and (e) induced electric field influences [11]).…”

Section: Introductionmentioning

confidence: 99%

“…Various explanations for Al oxidation mechanisms have also been proposed, each strongly tied to the ignition mechanism and heating rate [3]- [11]. All theories share a common theme for mass transport of fuel and oxidizer, but differ in how that diffusion is achieved (i.e., via (a) dispersion [3], [4], (b) phase changes in the polymorphous passivation shell [5]- [7] , (c) reactive sintering [8], (d) pressure gradient driven processes [9], [10], and (e) induced electric field influences [11]). This article will not directly deal with any particular reaction mechanism, but rather investigate the influence of a new parameter, mechanical strain, which has only recently been considered in the study of Al oxidation [3], [4], [12], [13].…”

Section: Introductionmentioning

confidence: 99%

Improving aluminum particle reactivity by annealing and quenching treatments: Synchrotron X-ray diffraction analysis of strain

2016

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In bulk material processing, annealing and quenching metals such as aluminum (Al) can relieve residual stress and improve mechanical properties. On a single particle level, affecting mechanical properties may also affect Al particle reactivity. This study examines the effect of annealing and quenching on the strain of Al particles and the corresponding reactivity of aluminum and copper oxide (CuO) composites. Micron-sized Al particles were annealed and quenched according to treatments designed to affect Al mechanical properties. Synchrotron X-ray diffraction (XRD) analysis of the particles reveals the thermal treatment increased the dilatational strain of the aluminum-core, alumina-shell particles. Flame propagation experiments also show thermal treatments effect reactivity when combined with CuO. An effective annealing/quenching treatment for increasing aluminum reactivity was identified. These results show that altering the mechanical properties of Al particles affects their reactivity. This manuscript focuses on synchrotron x-ray diffraction analysis of aluminum particles that have been treated to improve their mechanical properties. The aluminum is then examined for its reactivity with a metal oxide to show the relationship between material processing and the mechanical properties of the metal then extend this understanding towards application for energy generation technologies. We felt this combination of in-depth analysis of the material property of strain based on annealing and quenching processing of a metal powder and its application to reactivity were the perfect combination of mechanical and functional behavior appropriate for Acta Materialia. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 AbstractIn bulk material processing, annealing and quenching metals such as aluminum (Al) can relieve residual stress and improve mechanical properties. On a single particle level, affecting mechanical properties may also affect Al particle reactivity. This study examines the effect of annealing and quenching on the strain of Al particles and the corresponding reactivity of aluminum and copper oxide (CuO) composites. Micron-sized Al particles were annealed and quenched according to treatments designed to affect Al mechanical properties. Synchrotron Xray diffraction (XRD) analysis of the particles reveals the thermal treatment increased the dilatational strain of the aluminum-core, alumina-shell particles. Flame propagation experiments also show thermal treatments effect reactivity when combined with CuO. An effective annealing/quenching treatment for increasing aluminum reactivity was identified. These resultsshow that altering the mechanical properties of Al particles affects their reactivity.

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“…Although the NEMs are comprised of particles with primary sizes <100 nm, the question is, do nanoenergetic particles remain nano-sized during combustion or reaction? [3][4][5] Michael R. Zachariah mainly proposed that under high heating rates, NPs in NEMs would sinter into structures at larger size levels, before the bulk of the combustion can take place, which is also referred to as nanostructure loss, and is conrmed by theory and experiment. [3][4][5] Even so, increasing the interfacial contact between the metal and oxidizer NPs to a large extent still plays a decisive role in producing NEMs with high performance.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5] Michael R. Zachariah mainly proposed that under high heating rates, NPs in NEMs would sinter into structures at larger size levels, before the bulk of the combustion can take place, which is also referred to as nanostructure loss, and is conrmed by theory and experiment. [3][4][5] Even so, increasing the interfacial contact between the metal and oxidizer NPs to a large extent still plays a decisive role in producing NEMs with high performance. From the view point of the condensed phase interfacial reaction mechanism, 6,7 it is assumed that when the sintering is occurring between the metal and oxidizer NPs, it is an effective process; otherwise it is an unfavorable process.…”

Section: Introductionmentioning

confidence: 99%

A new strategy for the fabrication of high performance reactive microspheres via energetic polyelectrolyte assembly

Zhang

et al. 2017

RSC Adv.

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Since the thermite reaction in aluminum-based nanostructured energetic materials (NEMs) is closely involved with Al and oxide nanoparticles (NPs), intimate interfacial contact between the Al and oxide NPs is widely considered to be a key parameter for the NEMs with high reactivity. With the aim to overcome the disadvantage of inert modifiers without energetic groups, used in the assembly approach, which is a cutting-edge solution to precisely organize the arrangement of the Al and oxide NPs and lead to enhanced intimacy, we successfully prepared GAP-based (GAP, glycidyl azide polymer) energetic polyelectrolytes (GEPEs) and demonstrated electrostatic assembly as a facile way to fabricate high performance, reactive Al/Fe 2 O 3 microspheres after modification of the Al and Fe 2 O 3 NPs with the GEPEs.The pressurization rate of the obtained reactive microspheres, a relative measurement of the reactivity, reached 410.36 MPa s À1, which is the highest value obtained so far, and is 1-2 orders of magnitude higher than that of other reported Al/Fe 2 O 3 NEMs. The incorporated GEPEs serve three main roles:GEPEs act as a modifier by interacting strongly with the NPs, and improve the intimacy of the Al and Fe 2 O 3 via powerful electrostatic attraction between the modified NPs; the assembly of the reactive microspheres can be achieved through the directing assembly of the GEPEs themselves; internal gas released by the decomposition of energetic sites existing inside the assembled microspheres rapidly separates the NPs to prevent adverse sintering and to weaken the nanostructure loss during the reaction, resulting in an improvement of the reactivity.

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Do nanoenergetic particles remain nano-sized during combustion?

Cited by 116 publications

References 23 publications

A slice of an aluminum particle: Examining grains, strain and reactivity

A slice of an aluminum particle: Examining grains, strain and reactivity

Improving aluminum particle reactivity by annealing and quenching treatments: Synchrotron X-ray diffraction analysis of strain

A new strategy for the fabrication of high performance reactive microspheres via energetic polyelectrolyte assembly

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